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50 BC to 1960s : Not relevant: –Pre-computer: Caesar cipher to Enigma. Keys prearranged by hand 1960s to 1980s : Not considered necessary –ARPAnet, an open network, no or little secret, e.g. telnet. open relays A Quick History of Key Establishment and Authentication

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Model Checking Idea: –Make a model of your system with has a limited number of states –Check every single state to make sure its OK Problem: making the model finite Problem: “state space explosion” Very effective, many industrial applications

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Model Checking 1994 Pentium chip was missing a few entries in a table. Almost never used so missed by standard testing. If x=4195835 & y =3145727 then x/y=1.333739068902037589 rather than =1.333820449136241002 But x-(x.y/y)= 256 not 0

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Result Public relations disaster Jokes: –How many Pentium designers does it take to change a light bulb? –1.99995827903 100 of millions of dollars of replacement costs. Intel now model checks all hardware.